Resonant frequency separation for an actuator assembly of a disc drive

ABSTRACT

An actuator assembly is provided that includes a body portion, a first actuator arm assembly, a second actuator arm assembly, a first flexure assembly, and a second flexure assembly. Each of the first and second actuator arm assemblies projects from the body portion and has a distal end with different respective first and second mechanical configurations. Each of the flexure assemblies is respectively mounted to the distal ends of the first and second actuator arm assemblies. The first and second mechanical configurations are selected to provide the first and second flexure assemblies with different mechanical resonance characteristics. In a preferred embodiment, the second actuator arm assembly includes an actuator arm and a spacer disposed between the actuator arm and the second flexure assembly. The spacer has a stiffness different from the stiffness of the actuator arm.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/332,921 entitled FREQUENCY SEPARATION DAMPING filedNov. 14, 2001.

FIELD OF THE INVENTION

[0002] The claimed invention relates generally to moveable actuatorsystems and more particularly to actuator assemblies for disc drives.

BACKGROUND OF THE INVENTION

[0003] Data storage devices of the type known as “Winchester” discdrives are well known in the industry. These disc drives magneticallyrecord digital data on several circular, concentric data tracks on thesurfaces of one or more rigid discs. The discs are typically mounted forrotation on the hub of a spindle motor. The spindle motor is mounted toa base deck. In disc drives of the current generation, the discs arerotated at speeds of more than 10,000 revolutions per minute.

[0004] Data are recorded to and retrieved from the discs by an array ofvertically aligned read/write head assemblies, or heads, which arecontrollably positioned by an actuator assembly. Each head typicallyincludes electromagnetic transducer read and write elements which arecarried on an air bearing slider. The slider acts in a cooperativehydrodynamic relationship with a thin layer of air dragged along by thespinning discs to fly each head in a closely spaced relationship to thedisc surface. In order to maintain the proper flying relationshipbetween the heads and the discs, the heads are attached to and supportedby flexures (also called head suspensions).

[0005] A typical disc drive has an actuator assembly with more than onearm supporting a number of flexure assemblies. Any structure, such as anactuator assembly, that has several identical components can havebalanced modes of vibration. A balanced mode of vibration occurs for astructure when there is no net reaction force on the structure. Becausebalanced modes do not have a net reaction force acting on the structure,the vibration decay rate is determined solely by the individualidentical components making up the structure.

[0006] When the vibration modes of the individual components areseparated in frequency and when the remainder of the structure has highdamping, then there is a greater degree of damping than what is causedby each individual component. The vibration modes of the individualcomponents can be separated in frequency by making structural changes toeliminate the balanced modes.

[0007] When the vibration modes of the individual components, such asthe flexure assemblies, are close in frequency, the excitation of one ofthe flexure assemblies can couple to produce sympathetic motion in oneof the other flexure assemblies. If this occurs, the amplitude ofvibration becomes higher than it would be for only one flexure assembly.This increase in the amplitude of vibration can cause an increase in thetrack following error and the position error that affects the readingand writing performance. Depending on the vibration mode, the increasein the amplitude of vibration could also cause head-to-disk contact.Thus, it is highly desirable to cause the flexure assemblies havedifferent resonant frequencies.

[0008] One method for separating vibration modes of the individualcomponents is to make each flexure slightly different. U.S. Pat. No.5,953,180 issued to Frater et al. (Frater '180) presents severalalternative means of differentiating head/gimbal assemblies that share acommon actuator arm. Each head/gimbal assembly is made up of a flexure,a gimbal, a head, and the slider for the head. If there is sufficientdamping, these alternatives that Frater '180 disclose can be effective.However, providing different head/gimbal assemblies for each actuatorarm can be relative expensive and difficult to manage in a high volumemanufacturing environment.

[0009] Thus, there is a need for an improved actuator assembly thatovercomes these and other limitations of the prior art.

SUMMARY OF THE INVENTION

[0010] In accordance with preferred embodiments, an actuator assembly isprovided that includes a body portion, a first actuator arm assembly, asecond actuator arm assembly, a first flexure assembly, and a secondflexure assembly. Each of the first and second actuator arm assembliesprojects from the body portion and has a distal end with differentrespective first and second mechanical configurations. The flexureassemblies are nominally identical, and are respectively mounted to thedistal ends of the first and second actuator arm assemblies. The firstand second mechanical configurations are selected to provide the firstand second flexure assemblies with different mechanical resonancecharacteristics.

[0011] In a preferred embodiment, the second actuator arm assemblyincludes an actuator arm and a spacer disposed between the actuator armand the second flexure assembly. The spacer has a stiffness differentfrom the stiffness of the actuator arm.

[0012] In another preferred embodiment, the first actuator arm assemblyincludes a first actuator arm having a first mounting area to which thefirst flexure assembly is affixed. The second actuator arm assembly hasa second mounting area to which the second flexure assembly is affixed.The second mounting area is smaller than the first mounting area. Inthis preferred embodiment, a notch may be formed in the second actuatorarm to define the second mounting area.

[0013] These and various other features as well as advantages whichcharacterize the claimed invention will become apparent upon reading thefollowing detailed description and upon reviewing the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a plan view of a disc drive constructed in accordancewith preferred embodiments of the present invention.

[0015]FIG. 2 is a partial, section view of an actuator assembly of theprior art.

[0016]FIG. 3 is a partial section view of an actuator assemblyconstructed in accordance with preferred embodiments of the invention.

[0017]FIG. 4 is a partial section view of an actuator assemblyconstructed in accordance with preferred embodiments of the invention.

[0018]FIG. 5 is a partial section view of an actuator assemblyconstructed in accordance with preferred embodiments of the invention.

[0019]FIG. 6 is a partial section view of an actuator assemblyconstructed in accordance with preferred embodiments of the invention.

DETAILED DESCRIPTION

[0020]FIG. 1 provides a top plan view of a disc drive 100 constructed inaccordance with preferred embodiments of the present invention. A basedeck 102 and a top cover 104 (shown in partial cutaway) cooperate toform a sealed housing for the disc drive 100. A spindle motor with a hub106 rotates a number of magnetic recording discs 108 at a constant, highspeed. An actuator assembly 110 includes a number of rigid actuator arms(topmost shown at 112) that extend adjacent the disc surfaces. Flexures(topmost shown at 114) extend from the actuator arms 112 to support anarray of read/write heads 116. The actuator assembly 110 is pivotallymoved through the application of current to an actuator coil 118 of avoice coil motor (VCM) 120.

[0021]FIG. 2 shows a partial section view of an actuator assembly 110 ofthe existing art. In FIG. 2, nominally identical flexures 114, 115extend from nominally identical actuator arms 112, 113. The read/writeheads 116 are positioned at the end of the flexures 114, 115 to readdata from the disc 108 and write data to the disc 108. The first flexure114 is attached to the first actuator arm 112. The second flexure 115 isattached to the second actuator arm 113.

[0022]FIG. 3 shows an actuator assembly constructed in accordance withpreferred embodiments of the present invention. The actuator assembly110 includes a body portion 122, a first actuator arm assembly 124, asecond actuator arm assembly 126, a first flexure assembly 128 and asecond flexure assembly 130. The first actuator assembly 124 has a firstactuator arm 112 and the second actuator arm assembly 126 has a secondactuator arm 132.

[0023] The first actuator arm assembly 124 has a conventional actuatorarm 112 as is commonly found in actuator arms of the existing art. Thesecond actuator arm assembly 128 has an actuator arm 132 with a notch134 formed in an end 136 of the second actuator arm 132 distal from thebody portion 122. Each of the distal ends 136 of the first actuator armassembly 124 and the second actuator arm assembly 126 has a differentmechanical configuration. Because of the notch 134, a mounting area 135of the distal end 136 for attaching the second flexure assembly 130 tothe second actuator arm 132 is reduced, as compared with a mounting area135 of the first actuator arm 114.

[0024] The first flexure assembly 128 includes a first flexure 114 andthe second flexure assembly 130 includes a second flexure 138. Each ofthe flexure assemblies 128 and 130 also includes a head 116. Each of theflexure assemblies 128 and 130 is nominally identical to the other. Eachhead 116 reads data from the disc 108 or writes data to the disc 108.Each of the flexures 114 and 138 is attached to one of the actuator arms112 and 132, respectively, by an adhesive.

[0025] The reduced mounting area 135 for attaching the second flexure138 to the actuator arm 134 causes the second flexure assembly 130 tohave mechanical resonance characteristics different from the mechanicalresonance characteristics of the first flexure assembly 128. In general,the resonant frequencies of the first flexure assembly 128 are differentfrom the resonant frequencies of the second flexure assembly 130 becauseof the reduced mounting area 135 for the distal end of the secondactuator arm 132. In a mathematical model of the vibration of theflexure assemblies 128 and 130, this difference in mounting area 135 ismodeled as different boundary conditions for the equations of motion.

[0026]FIG. 4 shows another actuator assembly 110 having a body portion122, a first actuator arm assembly 124, a second actuator arm assembly126, a first flexure assembly 128 and a second flexure assembly 130. Thefirst actuator assembly 124 has a first actuator arm 112 and the secondactuator arm assembly 126 has a second actuator arm 132. The firstactuator arm 112 is a conventional actuator arm 114 as is commonly foundin actuator arms of the existing art.

[0027] The second actuator arm assembly 126 includes a spacer 140positioned between the second actuator arm 132 and the second flexureassembly 130. The spacer 140 is made from a material having a differentstiffness than the stiffness of the material that forms the actuatorarms 112 and 132. In a preferred embodiment, the spacer 140 is plasticand the actuator arms 112 and 132 are aluminum.

[0028] The first flexure assembly 128 includes a first flexure 114 andthe second flexure assembly 130 includes a second flexure 138. Each ofthe flexure assemblies 128 and 130 is nominally identical to oneanother. Each flexure assembly 128 and 130 includes a head 116. Each ofthe heads 116 reads data from the disc 108 or writes data to the disc108. Each of the flexures 114 and 138 is attached to one of the actuatorarms 112 and 132, respectively, by a swage interconnection 142.

[0029] The swage interconnection 142 for the second actuator arm 132 isformed by positioning a swage boss 144 through a hole in the secondflexure 142, through a void in the spacer 140 and through an opening ina distal end 136 of the second actuator arm 132. The swage boss 144 isconnected to swage plate 146. When the swage boss 144 is in place, aswage ball is passed through the swage boss 144 to deform the swage boss144 against walls of the actuator arm openings and against walls of theflexure holes. The deformation of the swage boss 144 secures the secondflexure 138 to the second actuator arm 132. The swage interconnection142 is similarly formed for the first actuator arm assembly 124, but thefirst actuator arm assembly 124 does not have a spacer 140.

[0030] Each of the distal ends 136 of the first actuator arm assembly124 and the second actuator arm assembly 126 has a different mechanicalconfiguration. The presence of the spacer 140 that has a differentstiffness than the stiffness of the actuator arm material causes thesecond flexure assembly 130 to have mechanical resonance characteristicsdifferent from the mechanical resonance characteristics of the firstflexure assembly 128. In general, the resonant frequencies of the firstflexure assembly 128 are different from the resonant frequencies of thesecond actuator arm assembly 130 because of the presence of the spacer140. In a mathematical model of the vibration of the flexure assemblies128 and 130, this difference of having a spacer 140 for the secondactuator arm assembly 126, and not the first actuator arm assembly 124,is modeled as different boundary conditions for the equations of motion.

[0031]FIG. 5 shows another actuator assembly 110 constructed inaccordance with a preferred embodiment of the present invention. In FIG.5, an actuator assembly 110 has a body portion 122, a first actuator armassembly 124, a second actuator arm assembly 126, a third actuator armassembly 150, a first flexure assembly 128, a second flexure assembly130, a third flexure assembly 152, and a fourth flexure assembly 154.The first actuator arm assembly 124 has a first actuator arm 112, thesecond actuator arm assembly has a second actuator arm 132, and thethird actuator arm assembly 150 has a third actuator arm 156.

[0032] The first actuator arm assembly 124 has a conventional actuatorarm 112 as is commonly found in actuator arms of the existing art. Thesecond actuator arm assembly 126 has an actuator arm 132 with a reducedmounting area 135 at a distal end 136 for attaching the second flexureassembly 130 and third flexure assembly 152 to the second actuator arm132, as compared with a mounting area 135 of the first actuator arm 114.

[0033] The third actuator arm assembly 150 includes a spacer 140positioned between the third actuator arm 156 and the fourth flexureassembly 154. The spacer 140 is made from a material having a differentstiffness than the stiffness of the material that forms the actuatorarms 112, 132, 156. In a preferred embodiment, the spacer 140 is rubberand the actuator arms 112, 132, 156 are aluminum.

[0034] The first flexure assembly 128 includes a first flexure 114, thesecond flexure assembly 130 includes a second flexure 138, the thirdflexure assembly 152 includes a third flexure 158, and the fourthactuator assembly includes a fourth flexure 160. Each of the flexureassemblies 128, 130, 152, 154 also includes a head 116. Each head 116reads data from the discs 108 or writes data to the discs 108. Each ofthe flexures 114,138, 158, 160 is attached to the actuator arms 112,132, 156 respectively, by a swage interconnection, as described abovefor FIG. 4. Each flexure assembly 128, 130, 152, 154 is nominallyidentical.

[0035]FIG. 6 shows another actuator assembly 110 constructed inaccordance with a preferred embodiment of the present invention. In FIG.6, an actuator assembly 110 has a body portion 122, a first actuator armassembly 124, a second actuator arm assembly 126, a third actuator armassembly 150, a first flexure assembly 128, a second flexure assembly130, a third flexure assembly 152, and a fourth flexure assembly 154.The first actuator arm assembly 124 has a first actuator arm 112, thesecond actuator arm assembly has a second actuator arm 132, and thethird actuator arm assembly 150 has a third actuator arm 156.

[0036] The first actuator arm assembly 124 has a conventional actuatorarm 112 as is commonly found in actuator arms of the existing art.

[0037] The second actuator arm assembly 126 has a second actuator arm132 with a spacer 140 positioned between the top side of the secondactuator arm 132 and the second flexure 138. The spacer 140 is made froma material having a different stiffness than the stiffness of thematerial that forms the actuator arms 112, 132, 156. A bottom side ofthe second actuator arm assembly 126 is configured as a conventionalactuator arm of the existing art for attaching the third flexureassembly 152 to the bottom side of the second actuator arm 132.

[0038] The third actuator arm assembly 150 includes a spacer 141positioned between the third actuator arm 156 and the fourth flexureassembly 154. The spacer 141 is made from a material having a differentstiffness than the stiffness of the material that forms the actuatorarms 112, 132, 156. In a preferred embodiment, the spacer 140 is rubber,the spacer 141 is plastic and the actuator arms 112, 132, 156 arealuminum.

[0039] The first flexure assembly 128 includes a first flexure 114, thesecond flexure assembly 130 includes a second flexure 138, the thirdflexure assembly 152 includes a third flexure 158, and the fourthflexure assembly includes a fourth flexure 160. Each of the flexureassemblies 128, 130, 152, 154 also includes a head 116. Each head 116reads data from the discs 108 or writes data to the discs 108. Each ofthe flexures 114,138, 158, 160 is attached to the actuator arms 112,132, 156 respectively, by a swage interconnection, as described abovefor FIG. 4. Each flexure assembly 128, 130, 152, 154 is nominallyidentical.

[0040] For the embodiments shown in FIGS. 5 and 6, each of the flexureassemblies 128, 130, 152, 154 generally has different vibration andmechanical resonance characteristics. If one wished to add more actuatorarms, one could provide another actuator assembly with a spacer having adifferent stiffness than the spacers 140, 141 used for the second andthird actuator assemblies 126, 150. Alternatively, one could provide anactuator assembly such as the second actuator arm assembly 126 having anotch of a different size than the notch of the second actuator armassembly 126 so that the mounting area 135 of the distal end of theactuator arm is also different.

[0041] Accordingly, an actuator assembly (such as 110) is provided thatincludes a body portion (such as 122), a first actuator arm assembly(such as 124), a second actuator arm assembly (such as 126), a firstflexure assembly (such as 128), and a second flexure assembly (such as130). Each of the first and second actuator arm assemblies projects fromthe body portion and has a distal end (such as 136) with differentrespective first and second mechanical configurations. Each of theflexure assemblies is respectively mounted to the distal ends of thefirst and second actuator arm assemblies. The first and secondmechanical configurations are selected to provide the first and secondflexure assemblies with different mechanical resonance characteristics.

[0042] In a preferred embodiment, the second actuator arm assemblyincludes an actuator arm and a spacer (such as 140) disposed between theactuator arm and the second flexure assembly. The spacer has a stiffnessdifferent from the stiffness of the actuator arm.

[0043] In another preferred embodiment, the first actuator arm assemblyincludes a first actuator arm having a first mounting area (such as 135)to which the first flexure assembly is affixed. The second actuator armassembly has a second mounting area to which the second flexure assemblyis affixed. The second mounting area is smaller than the first mountingarea. In this preferred embodiment, a notch (such as 134) may be formedin the second actuator arm to define the second mounting area. For allembodiments, the flexure assemblies are nominally identical.

[0044] In yet another preferred embodiment, the actuator assembly isused in a disc drive (such as 100). In this embodiment, each flexureassembly includes a flexure (such as 114, 138) and a head (such as 116).The head writes data to and reads data from a disc (such as 108). Forall embodiments, the flexure assemblies are nominally identical.

[0045] It is to be understood that even though numerous characteristicsand advantages of various embodiments of the present invention have beenset forth in the foregoing description, together with details of thestructure and function of various embodiments of the invention, thisdetailed description is illustrative only, and changes may be made indetail, especially in matters of structure and arrangements of partswithin the principles of the present invention to the full extentindicated by the broad general meaning of the terms in which theappended claims are expressed. For example, the particular elements mayvary depending on the particular application of the actuator assemblywithout departing from the spirit and scope of the present invention.

[0046] The claims below include steps for mounting a flexure to anactuator arm. Although the steps are listed in a particular order, thisdoes not mean that the steps must be carried out in the order the stepsare listed. The only order that may be inferred from the claims is forthe steps that must be accomplished before other steps can beaccomplished.

[0047] In addition, although the embodiments described herein aredirected to an actuator assembly for a disc drive, it will beappreciated by those skilled in the art that the actuator assembly canbe used for other devices without departing from the scope of theclaimed invention.

What is claimed is:
 1. An actuator assembly, comprising: a body portion;first and second actuator arm assemblies which project from the bodyportion and which have distal ends with different respective first andsecond mechanical configurations; and first and second flexureassemblies respectively mounted to the distal ends of the first andsecond actuator arm assemblies, wherein the first and second mechanicalconfigurations are selected to provide the first and second flexureassemblies with different mechanical resonance characteristics.
 2. Theactuator assembly of claim 1, wherein the second actuator arm assemblycomprises an actuator arm and a spacer disposed between the actuator armand the second flexure assembly.
 3. The actuator assembly of claim 2wherein the spacer has a stiffness different from a stiffness of theactuator arm.
 4. The actuator assembly of claim 1, wherein the firstactuator arm assembly comprises a first actuator arm having a firstmounting area to which the first flexure assembly is affixed, whereinthe second actuator arm assembly comprises a second actuator arm havinga second mounting area to which the second flexure assembly is affixed,and wherein the second mounting area is smaller than the first mountingarea.
 5. The actuator assembly of claim 4, wherein a notch is formed inthe second actuator arm to define the second mounting area.
 6. Theactuator assembly of claim 1, wherein the first and second flexureassemblies are nominally identical.
 7. The actuator assembly of claim 1,wherein the first and second flexure assemblies respectively comprisefirst and second data transducing heads in a disc drive.
 8. The actuatorassembly of claim 1, wherein swage interconnections are used to affixthe first flexure assembly to the first actuator arm assembly and toaffix the second flexure assembly to the second actuator arm assembly.9. The actuator assembly of claim 1, wherein adhesive is used to affixthe first flexure assembly to the first actuator arm assembly and toaffix the second flexure assembly to the second actuator arm assembly.10. The actuator assembly of claim 1, wherein the body portion isrotatable about an actuator axis which extends substantially normal to adirection along which the first and second actuator arm assembliesextend.
 11. The actuator assembly of claim 2 further comprising a thirdflexure assembly mounted to the distal end of the second actuator arm,wherein the second flexure is mounted to a top side of the secondactuator arm and the third flexure is mounted to a bottom side of thesecond actuator arm.
 12. A disc drive, comprising: first and secondflexure assemblies; first means for supporting the first flexureassembly; and second means for supporting the second flexure assembly,wherein the second means provides mechanical response characteristicsdifferent from mechanical response characteristics provided to by thefirst means.
 13. The disc drive of claim 12, wherein the first meanscomprises a first actuator arm assembly having a distal end with a firstmechanical configuration and wherein the second means comprises a secondactuator arm assembly having a distal end with a second mechanicalconfiguration different from the first mechanical configuration.
 14. Thedisc drive of claim 13, wherein the second actuator arm assemblycomprises an actuator arm and a spacer disposed between the actuator armand the second flexure assembly.
 15. The disc drive of claim 14 whereinthe spacer has a stiffness different from a stiffness of the actuatorarm.
 16. The disc drive of claim 13, wherein the first actuator armassembly comprises a first actuator arm having a first mounting area towhich the first flexure assembly is affixed, wherein the second actuatorarm assembly comprises a second actuator arm having a second mountingarea to which the second flexure assembly is affixed, and wherein thesecond mounting area is smaller than the first mounting area.
 17. Thedisc drive of claim 12, wherein the first and second flexure assembliesare nominally identical.
 18. The disc drive of claim 12 wherein thefirst flexure assembly is attached to a top side of an actuator arm andthe second flexure assembly is attached to a bottom side of the actuatorarm.
 19. A method for forming an actuator, comprising: providing firstand second actuator arm assemblies having different, respective firstand second mechanical configurations; providing first and second flexureassemblies; affixing the first flexure assembly to the first actuatorarm assembly; and affixing the second flexure assembly to the secondactuator arm assembly, wherein the second mechanical configurationresults in the second flexure assembly having different mechanicalresponse characteristics as compared to mechanical responsecharacteristics of the first flexure assembly.
 20. The method of claim19, wherein the providing first and second flexure assemblies stepcomprises providing nominally identical first and second flexureassemblies.
 21. The method of claim 19, wherein the providing first andsecond actuator arm assemblies step comprises providing the secondactuator arm assembly with a spacer that is disposed between the secondflexure assembly and a second actuator arm of the second actuator armassembly during the affixing the second flexure assembly step.
 22. Themethod of claim 19, wherein the providing first and second actuator armassemblies step comprises forming a notch in a second actuator arm ofthe second actuator arm assembly to reduce a flexure mounting area ofthe second actuator arm as compared to a flexure mounting area of afirst actuator arm of the first actuator arm assembly.